Method for improving soil

ABSTRACT

A method for treating soil to fix a harmful metal contained therein which is characterized in that to soil containing a harmful metal ion is added at least one of mercapto-s-triazines and water-soluble salts thereof.

United States Patent [191 Nakamura et al. Aug. 26, 1975 METHOD FOR IMPROVING SOIL [58] Field of Search 71/93, 64 SC [75] Inventors: Yoshiro Nakamura, Morioka; Akira Umehara, Osaka; ltsuyo Yamada, [56] References Cited of Japan UNITED STATES PATENTS [73] Assignee: Sankyo Kasei Company, Ltd., Japan 2.996.505 8/196! Schwarzc .v 71/93 X [22] Filed: June 18, 1974 [2]] App]. No: 480.465

Related US. Application Data [63] Continuation of Ser. No. 280.35]. Aug. 14 I972.

[5 l] Int. Cl. COSC 11/00 Primary ExaminerCharles N. Hart Attorney. Agent, or FirmToren, McGeady and Stanger [57] ABSTRACT A method for treating soil to fix a harmful metal con tained therein which is characterized in that to soil containing a harmful metal ion is added at least one of mercapto-s-triazines and water-soluble salts thereof.

7 Claims, No Drawings METHOD FOR IMPROVING SOIL This is a continuation of application Ser. No. 280,351 filed Aug. I4, 1972, now abandoned.

This invention relates to a method for improving soil, more particularly to a method for treating soil containing harmful metals therein.

With the recent development of industries, harmful metal ions such as Cd, Hg, Pb, etc. discharged from the industries have gradually accumulated in the soil. In al kaline soil, such metal ions produce no problem since they are fixed in the soil in the form of stable hydroxides. ln acidic or neutral soil, however, they are liable to be absorbed into plants and then to animals through the plants, resulting in death of the trees and various animal diseases.

Therefore, it is essential that the metal ions contaminating the soil be removed therefrom or fixed therein in a stable state. However, no successful method has been developed yet to accomplish this.

A main object of the invention is accordingly to pro vide a method for treating soil which makes it possible to fix harmful metal ions contained in acidic or neutral soil in a stable state, thereby rendering the metal unable to be ionized to avoid absorption by plants.

The method for treating soil is characterized in that to soil containing a harmful metal ion is added at least one of mercapto-s-triazines and water-soluble salts thereof, said mercapto-s-triazine having the formula,

(wann wherein R is hydrogen, NH OH, alkyl having 1 to 8 carbon atoms, alkoxy having l to 8 carbon atoms, phenyl, cyclohexyl, oxazinyl, phenoxy, NR' or SR", R being hydrogen. alkyl having l to 8 carbon atoms, phenyl, cyclohexyl, naphthyl or benzyl, R" being alkyl having 1 to 8 carbon atoms, phcnyl, cyclohexyl, naphthyl or benzyl; m is an integer of l to 3 and n is O or an integer of l to 2.

The researchers of the present inventors revealed that when the above specific triazine derivative is added to soil, it reacts with a harmful metal ion contained in the soil to produce a stable compound which will never form metal ion nor be absorbed to plants. Thus the harmful metal ion is effectively fixed. Further. it has been found according to the researches of the present inventors that the above s-triazine derivatives have such a peculiar selectivity in that they react with metal ions having a normal electrode potential of at least ().44() V (at 25C) but not with metal ions having a lower normal electrode potential. According to the present invention, therefore, various harmful metal ions having a normal electrode potential not lower than ().44() V (at 25C) such as Ag*, Cd, Pb, Hg, Cu, Sn, Ni, Fe and Fe*"* can be effectively fixed by the s'triazine derivatives of the invention, but metal ions which are essential to growth of plants and have lower normal electrode potential, such K. (a Mg remain in the soil as they are. Thus the soil is effectively improved.

The striazinc derivatives used in the invention are a mcrcapto-s'tria/ine represented by the above formulas (l) and a \vater solublc salt thereof, such as, an alkali metal salt, ammonium salt and alkaline earth metal salt. The mercapto-s-triazine includes a monomercaptostriazine, dimercapto-s-triazine and trimercapto-striazine. Of these the preferable salts are diand trimercapto-s-triazines and water-soluble salts thereof. These compounds are stable and undergo no change when left to stand in the air for a long period of time. It is not required for the s-triazine derivatives to have a high solubity in water. provided that they will be dissolved in water in a minimum amount necessary for adsorbing metal ions in the water. The mono-, diand trimercapto-s-triazines and the alkali metal, ammonium and alkaline earth metal salts thereof are usually dissolved in water in a concentration of 0.01 to 25 wtP/r at 25f', which is sufficient for the purpose.

Examples of the s-triazine derivatives are as follows:

A. Monomercapto-s-triazines and water-soluble salts thereof SH SH Site Skin 51! B. Dimercapto-s-triazines and water-soluble salts thereof:

NaENK TBB Han/TH N SNa r,

HS\/N Na Has SNa ns sii Mo NH-C2H5 im-cH c H N C Trimerea to-s-triuzincs and water-soluble salts NaS \n/sm 85% W- S P K L/ thereof:

N N N H N Hg YY -s ENE MN\[r c B \"/SH These compounds are odorless and stable and easily N N v available in the art. Further. the compounds have hac- (15 teriocidal action, so that they prevent the conversion of ammonia nitrogen to nitrate nitrogen due to action of 5 6 5 haste ria.

The method of the invention is applicable to acidic or neutral soil containing at least one of metel ions having a normal electrode potential of at least -().440 V (at C). Particularly the present method is effective for acidic soil having a pH value of 4.0 to 6.5. The metal ions having a normal potential of at least -().440 V (at 25C and to be fixed by the present invention in clude. for example. Au; Ag", Cd. Pb. Hg. Cu. Sn. Ni. Fe. FF. etc.

in amounts specified in Table l below. After being vigorously mixed in a barrel mixer for 60 minutes, the samples were washed with 500 ml ofa 2% aqueous solution of citric acid for 60 minutes. The concentration of heavy metal ions in the solution was measured in accordance with the atomic absorption analysis disclosed in HS 0102 1971 to determine the concentration of residual ions in the soil. The results are shown in Table 1 below.

The s-triazine derivatives of the invention can be applied to soil by various methods. for example. by sprinkling the compound in the form of an aqueous solution or dispersion, by sprinkling the compound with a fertilizcr or by mixing the compound with soil in combina' tion with powdery fillers, such as. lime, diatomace earth, etc. Of these methods, it is particularly preferable to apply the compound in the form of an aqueous solution or dispersion.

The amount of s-triazine derivatives to be used in the invention can vary over a wide range in accordance with the kinds of metal ions to be removed and triazinc derivatives to be used. The triazine derivatives may usually be added to the soil in such an amount as to provide at least one mercapto group per valence of the metal ion. Excess amount of the s-triazine derivatives can be used without any adverse effect. since the compounds have substantially no toxicity and harmful effects on human being as well as on animals and plants. However a largely excessive amount thereof gives no improved effect. so that it is preferable to use the compound in an amount less than ll) moles per valence of the metal ions. Particularly preferable amount is in the range of l to 3 moles per valence of the metal ions.

The metals fixed according to the present invention remain in a very stable form in the soil and never release metal ions.

For a better understanding of the invention examples are given below, in which ppm. and 2? are all by weight. Metal ion concentration in non-treated soil was determined as follows: to 10 g of a soil sample was added 50 ml of 0.1 N hydrochloric acid and the mixture was stirred at C for (10 minutes. After the mixture was filtered, metal ion concentration in the filtrate was determined by atomic absoprtion analysis as disclosed in HS U102 I971.

EXAMPLE 1 [00 g of air-dried soil samples having a diameter less than 2000 a contaminated with various heavy metal ions were uniformly sprinkled with 30 ml of water and to the soil samples was added monosodium salt of 2.4.b-trimcrcapto-s-triazine trihydratc s N H l H y m) EH20 SNa Table 2 20; Aqueous solu Aqueous solution Soil tion of citric of nitric acid No. acid {pH 2| Water I Nonc Trace None 2 None None None None None None 4 None None None From Table 2 above, it is apparent that heavy metals fixed in the soil according to the present invention as the insoluble products are very stable.

EXAMPLE 2 20 ml of a 0.1% aqueous solution of magnesium salt of 2,4,6-trimercapto-s-triazine (a mixture of and was sprinkled on l()() g of an air-dried soil of pH 5.0 having a diameter less than 2000 p containing 6 p.p.m. of Pb and 19 ppm. of Cu. After the soil was left to stand for l day, the concentration of residual metal ions in the soil was determined as in Example l. The results are given in Table 3 below.

Table 3 ('nlicentralion of residual metal ion III the soil to n m.|

From Table 3 above it is apparent that the present invention is effective for fixing heavy metal ions in soilv EXAMPLE 3 20 ml of a 0.1% aqueous solution of monosodium salt of 2.4.fi-trimercapto's-triazinc N H51: \JSH EXAMPLE 4 20 ml of a 0.0571 aqueous solution of trisodium salt of 2,4.o-trimercapto-s-triazine was sprinkled on I g of an air-dried soil sample having a diameter less than 2000 p. containing p.p.m. of Hg. After being vigorously stirred in a barrel mixer for 60 minutes. 10 g of the soil was shaken with 50 ml of 0. IN hydrochloric acid and the concentration of residual Hg in the soil was determined as in Example l. The residual Hg" was less than 0.0] Pnm.

Vl'hat we claim is:

l. A method tor treating soil to fix harmful metal ions having a normal electrode potential of at least ().440 at 25% contained therein which is characterized in that to such soil is added at least one of mcrcapto-striazines and water-soluble salts thereof. said mercapto-s-tria/ine having a formula of l wherein R is hydrogen. NH OH, alkyl having 1 to 8 carbon atoms, alkoxy having l to 8 carbon atoms phcnyl, cyclohcxyl. oxazinyl, phenoxy, NR' or SR". R, being hydrogen alkyl having I to 8 carbon atoms. phenyl, cyclohexyl naphthyl or benzyl, R" being alkyl having 1 to 8 carbon atoms. phenyl, cyclohexyl naphthyl 0r benzyl; m is an integer of l to 3 and n is 0 or an integer of 1 to 2.

2. The method according to claim 1, in which said mercapto-s-triazine is a monomercapto-s-triazine,

3. The method according to claim I, in which said mercapto-s-triazine is a dimercapto-s-triazine.

4. The method according to claim I, in which said mercapto-s-triazine is a trimercapto-s-triazinc.

5. The method according to claim 1, in which said water-soluble salt of mercapto-s-triazine is an alkali metal salt of mercapto-striazine. ammonium salt of mercapto-s-triazine or alkaline earth metal salt of mercapto-s-triazine.

6. The method according to claim I. in which said water-soluble salt of mercapto-s-triazine is added to the soil in an amount of l to 3 moles per valence of the metal ion removed.

7. The method according to claim l, in which said soil to he treated has a pH value of 4.0 to 6.5. 

1. A METHOD FOR TREATING SOIL TO FIX HARMFUL METAL IONS HAVING A NORMAL ELECTRODE POTENTIAL OF AT LEAST -0.440V AT 25*C. CONTAINED THEREIN WHICH IS CHARACTERIZED IN THAT TO SUCH SOIL IS ADDED AT LEAST ONE OF MERCAPTO-S-TRIAZINES AND WATER-SOLUBLE SALTS THEREOF, SAID MERCAPTO-S-TRIAZINE HAVING A FORMULA OF
 2. The method according to claim 1, in which said mercapto-s-triazine is a monomercapto-s-triazine.
 3. The method according to claim 1, in which said mercapto-s-triazine is a dimercapto-s-triazine.
 4. The method according to claim 1, in which said mercapto-s-triazine is a trimercapto-s-triazine.
 5. The method according to claim 1, in which said water-soluble salt of mercapto-s-triazine is an alkali metal salt of mercapto-s-triazine, ammonium salt of mercapto-s-triazine or alkaline earth metal salt of mercapto-s-triazine.
 6. The method according to claim 1, in which said water-soluble salt of mercapto-s-triazine is added to the soil in an amount of 1 to 3 moles per valence of the metal ion removed.
 7. The method according to claim 1, in which said soil to be treated has a pH value of 4.0 to 6.5. 